Field
Embodiments of the disclosure relate generally to aircraft structures and more particularly to embodiments for a one piece inlet skin having integral structural stiffeners on the inner mold line.
Background
Current aircraft structures for nacelle and engine cowlings employ skin elements stiffened with attached structural frames having a desired cross section for necessary support of the skin. Attachment of such structural frames requires numerous fasteners and creates significant time in assembly. Lip skins are critical aerodynamic surfaces and it is generally understood that a long lip skin is advantageous to preclude the necessity for a joint with the outer barrel far forward where disruption of the laminar flow region of the lip skin may occur. With the distance between the forward bulkhead outer attachment and the lipskin to outer barrel attachment being quite long, common practice has been to use a circumferential stiffener fastened to the inner mold line (IML) of the lipskin between the two joints to stiffen the panel. Such stiffeners have the problem that they are fastened with countersunk fasteners and the fasteners themselves, even though they are countersunk, cause disruptions in smoothness of the skin and disrupt laminar flow. Moreover, mechanically fastened stiffeners tend to be quite tall and are not integral to the skin, which may cause a large temperature difference between the outside of the skin and the inner chord of the stiffener when there is a thermal gradient. Also, a complete circumferential stiffener around the entire lip skin is heavy in order to have adequate stiffness for a step loading. However, the complete circumferential stiffener has been preferable since having only a partial circumferential stiffener and ending the stiffener in the middle of a panel may not provide desired fatigue properties. A mechanically fastened longitudinal stiffener results in similar problems with disrupting laminar flow and typically requires fasteners even farther forward than a circumferential ring stiffener.
It is therefore desirable to provide structurally simpler means of stiffening lip skins without aerodynamic impacts.